Torsional vibration dampers are used to limit the torsional vibrations that occur in a crankshaft of an internal combustion engine. Such dampers generally comprise an annular inertia member disposed within an annular chamber in a housing. A space between a wall of the chamber and the inertia member is filled with viscous damping fluid and the resistance to shear of the fluid between the chamber wall and the inertia member provides a damping effect.
One method of manufacturing this type of damper utilizes a sheet metal fabrication construction. The housing of such dampers generally comprises a two part construction. Typically each part comprises a central radial flange by which the damper is attached to the crankshaft and an outer region which is shaped to form the chamber. The parts are connected together such that the radial flanges are substantially coterminous and overlie one another and the outer regions combine to define the chamber.
One known torsional damper comprises a three component housing. The first two components are assembled to form a common radial flange as described above, and an outer region in the form of an annular channel. The annular inertia member is received in the channel and a third component in the form of a cover plate is fitted to cover the channel and seal the inertia member therein. The channel has an annular reservoir in which the viscous damping fluid is retained. Such an arrangement is simpler to manufacture than a two-component housing and is particularly advantageous in that the first component forming an outer wall of the channel can be made to a standard size whereas the second component can be made to various sizes to accommodate different sized annular inertia members for different damping criteria.
The cover plate is simply placed on the top edge of the walls of the channel and is fixed thereto at the junction between the walls and the cover plate by means of an electron beam weld or the like. When the damper is operational, the joints between the channel walls and the cover plate are subject to a relatively large amount of stress. In order to counteract this it has been known to increase the structural integrity by adding a large annular fillet weld in a corner of the channel at the flange where the first and second components meet. The use of a large fillet weld, however, can create distortion in the shape of the housing as a result of the significant heat produced in the welding process. Moreover, the fillet weld has to be machined to form the annular reservoir for the viscous damping fluid resulting in an increase in the manufacturing time and complexity.
It is an object of the present invention to obviate or mitigate the aforesaid disadvantages.